1. Field of the Invention
The present invention relates to an optical fiber sheet obtained by arranging an optical fiber inside a sheet, and a manufacturing method therefor.
2. Description of the Related Art
Optical fiber sheets used for providing optical fibers in an optical device generally have a configuration such that an optical fiber is placed and adhered between upper and lower resin sheets which having flexibility. However, at a portion where the optical fiber extends from the edge of the sheet, that is, at an end of the optical fiber sheet, a bending force acts on the optical fiber, so that there is the likelihood of damage or characteristic deterioration occurring in the optical fiber. Therefore, reinforcement of the optical fiber is attempted by placing a reinforcing tube over the optical fiber.
For the optical fiber reinforcing structure using a reinforcing tube, it can be considered to connect the end of the reinforcing tube placed over the optical fiber and the end of the sheets by bonding. However, since the end of the reinforcing tube and the end of the sheets are simply bonded, the reinforcing tube may be bent at the portion bonded with the end of the sheets due to the weight of the reinforcing tube itself, giving an increase a transmission loss, or the reinforcing tube is likely to come off from the sheets due to adhesive failure at the bonded portion.
Conventionally, therefore, a fiber reinforcing structure, for example as shown in FIG. 44A to FIG. 44C, is provided at the bonded portion of the reinforcing tube and the sheet. In this fiber reinforcing structure, after the end of a reinforcing tube 1 and the ends of sheets 2 of an optical fiber sheet 6 are connected by bonding (the bonded portion is indicated by reference symbol 3), a reinforcing sheet 4 is further secured by bonding so as to cover the vicinity of the bonded portion 3 from one side or both sides (in the figure, from one side), to thereby reinforce an optical fiber 5 (reinforce the portion extending from the edge of the sheet 2). In the figure, only one optical fiber 5 is shown in the optical fiber sheet 6, but normally, there is a plurality of fibers. Moreover, the optical fiber 5 may be arranged in a curvilinear form, rather than in a linear form.
However, when the vicinity of the bonded portion 3 is reinforced by the reinforcing sheet 4, while this prevents the reinforcing tube 1 from being bent or coming off from the sheet 2 at the base thereof, it causes a problem in that other portions are easily bent due to the weight of the reinforcing sheet 4.